The present invention relates to hard ceramic materials, particularly to a process for synthesizing hard ceramic material, and more particular to such a process that involves sputter deposition of alternating layers of reactive metals with layers of material, such as carbon, boron or aluminum and the subsequent reaction of the multilayered structure to produce a dense crystalline ceramic.
Borides and carbides are well known as hard ceramic materials commonly used for engineering applications that are subject to erosion, corrosion and high temperatures. Also, films of such ceramics and intermetallic are coated on other materials to improve their performance, such as in machine tool applications.
Ceramics, intermetallics and composites have been synthesized in exothermic chemical reactions. Normally, the reactants are blended together as powders, pressed into an appropriate shape and ignited. This causes a combustion wave to rapidly self-propagate through the reactants transforming them into the final product. The combustion synthesis of powder reactants generally produces a bulk product of coarse powders or monolithic pieces that require additional processing into a final usable form.
Where films of the ceramic and intermetallic materials are coated of other materials, several variations of two vapor deposition techniques have been used as commercial processes to apply the coating. These two vapor deposition techniques are chemical vapor deposition (CVD) and physical vapor deposition (PVD). Prior efforts to produce such films or coatings, are exemplified by the following U.S. Patents:
The Bergmann et al. U.S. Pat. No. (4,992,153 issued Feb. 12, 1991) discloses a sputter--CVD process for coating a workpiece wherein carbide containing layers, among other, are formed.
The Garg et al. U.S. Pat. No. (4,902,535 issued Feb. 20, 1990) discloses a method for depositing hard coatings on titanium or titanium alloys wherein a non-reactive noble metal interlayer is deposited using electroless platin and a hard outer coating is deposited onto that interlayer using vapor deposition techniques.
The dos Santos Pereina Ribeiro U.S. Pat. No. (4,883,574 issued Nov. 28, 1989) discloses a method of applying coatings to objects using magnetic field supported cathode sputtering in a vacuum.
The Boss U.S. Pat. No. (4,849,081 issued Jul. 18, 1989) discloses a method for forming oxide films by reactive sputtering of silicon, titanium, aluminum or tin in an oxygen-containing atmosphere.
The Haluska et al. U.S. Pat. No. (4,822,697 issued Apr. 18, 1989) discloses a method wherein one or more ceramic coatings containing silicon carbide, silicon nitrogen, or silicon carbon nitrogen are applied over a ceramified SiO.sub.2 coating and a CVD or PECVD top coating is applied for further protection.
The Keem et al. U.S. Pat. No. (4,724,169 issued Feb. 9, 1988) discloses a method of producing multilayer coatings on a substrate wherein one layer may provide hardness or wear resistance. In a specific embodiment, the coatings comprise an oxidation resistance layer, a nitride layer, and a layer of disordered boron and carbon material.
The Goebel et al. U.S. Pat. No. (4,371,570 issued Feb. 1, 1983) discloses a method for producing a coated article which provides protection against hot corrosion at moderate temperatures. Physical vapor deposition can be used to produce the coating.
While the various prior art processes have served to advance this field of technology, it has been discovered that by combining two prior art processes; namely, sputter deposition and synthesis, using multilayer materials, hard ceramic foils or films can be produced. The process of this invention involves the sputter deposition of alternating layers of reactive metals with layers of carbon, boron or aluminum, and the subsequent reaction (synthesis) of the multilayered structure to produce a dense crystalline ceramic. Ceramic composites, as well as coatings on other materials, such as selected tools may be provided by this invention. The thus produced materials may also find use in extreme environments involving erosion, corrosion, wear, and high temperature.